Rankine cycle mid-temperature recuperation

ABSTRACT

A system and method for recuperation is provided including a boiler wherein air and exhaust gas recirculation pass through the boiler and are cooled by thermal transfer with a coolant. The system includes an expander receiving coolant from the boiler, a recuperator receiving coolant from the expander, a condenser receiving coolant from the recuperator; a pump pumping coolant from the condenser to a low temperature portion of the boiler, and a valve, which allows coolant to pass directly from the boiler to the recuperator.

BACKGROUND

When a Rankine Cycle Waste Heat Recovery (RC-WHR) is applied to airsystems (both clean air and EGR), it preferably delivers target airtemperatures to be reached for engine emissions compliance. It alsotries to achieve as high a cycle efficiency as possible for example toimprove engine Brake Specific Fuel Consumption (BSFC). Additionally,recuperation is often desired to help increase the cycle efficiency,regardless, when very dry fluids with narrow P-h dome are used ascoolant. However, with a recuperator for energy exchange betweenpump-out coolant and exhaust from expander in the conventional RC-WHRsystem, the amount of recuperation, which is limited by the coolanttemperature flowing out of recuperator, is constrained by the target airtemperature. This constraint limits the cycle efficiency and bsfcimprovement from RC-WHR system.

SUMMARY

One or more embodiments provide a system and method for recuperationincluding a boiler wherein air and exhaust gas recirculation passthrough the boiler and are cooled by thermal transfer with a coolant.The system includes an expander receiving coolant from the boiler, arecuperator receiving coolant from the expander, a condenser receivingcoolant from the recuperator, a pump pumping coolant from the condenserto a low temperature portion of the boiler, and a valve, which allowscoolant to pass directly from the boiler to the recuperator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional recuperation system.

FIG. 2 illustrates the recuperation system of FIG. 1 in greater detail.

FIG. 3 illustrates a modified recuperation system.

FIG. 4 illustrates the modified recuperation system of FIG. 3 in moredetail.

FIG. 5 illustrates the previous recuperator configuration operating atC100.

FIG. 6 illustrates the new recuperator configuration operating at C100.

FIG. 7 illustrates the new recuperator configuration operating at C100and also at supercritical.

FIG. 8 illustrates the prior recuperator configuration operating at B50.

FIG. 9 illustrates the new recuperator configuration operating at B50.

FIG. 10 illustrates the new recuperator configuration operating at B50and also at supercritical.

DETAILED DESCRIPTION

FIG. 1 illustrates a conventional recuperation system 100. Therecuperation system 100 includes an air plus exhaust gas recirculation(EGR) 110, a boiler 120, an expander 130, a recuperator 140, a condenserloop 145, a condenser 150, a pump 160, and an intake manifold 170.

In operation, air plus EGR 110 is fed into the boiler 120. An expander130 is in fluid connection with the boiler and a recuperator 140.Coolant flows from the boiler 120 to the expander 130 and then to therecuperator 140. Some coolant passes from the recuperator 140 into thecondenser loop 145 where the coolant then passes through the condenser150 and is pumped by pump 160 back to the recuperator 140. Finally,coolant passes from the recuperator 140 back to the boiler 120. Thecoolant in the boiler 120 acts to reduce the temperature of the air plusEGR 110 until the desired temperature at the intake manifold isachieved.

FIG. 2 illustrates the recuperation system 100 of FIG. 1 in greaterdetail. FIG. 2 includes the boiler 120, the expander 130, therecuperator 140, the air cooled condenser 150 and the pump 160 of FIG. 1and additionally includes a transmission 180, an integrated startergenerator (ISG) 182, an Inverter and Control 184, a turbogenerator 186,a high temperature radiator 188, an A/C condenser 190, and anaccumulator 192.

FIG. 3 illustrates a modified recuperation system 200. The modifiedrecuperation system 200 includes an air plus exhaust gas recirculation(EGR) 210, a boiler 220, an expander 230, a recuperator 240, a condenserloop 245, a condenser 250, a pump 260, an intake manifold 270, amulti-position three-way valve 265, and an intake manifold 270. Themodified recuperation system 200 of FIG. 3 provides the ability to applyRankine Cycle-Waste Heat Recycling (RC-WHR) systems to the air system(both clean air and EGR) and develop a match between dry fluids and sucha RC system is a new and developing area.

More specifically, instead of plumbing or piping the coolant (orrefrigerant) from the pump 260 directly to the recuperater 240, thecoolant is first directed to the low temperature section of heatexchanger (boiler) 220. After heated up to a certain degree, therefrigerant is routed to recuperator 240 for recuperation, and thenintroduced back to boiler 220 for further heating. By piping the coolantin this way, the target temperature is not a constraint to recuperationany more. By adding a multi-position 3-way valve 265, the targettemperature may be easily assured. For example, the temperature in theintake manifold 270 may be measured using a temperature sensor 268. Datafrom the temperature sensor 260 may be passed to a valve control 267 todetermine the settings for the valve 265, that is whether the valveshould be opened more, closed more, or remain in the same setting so asto deliver the desired temperature at the intake manifold 270.

Consequently, by carefully designing the two sections of the boiler 120,a larger amount of energy may be recuperated, thus increasing the cycleefficiency and providing a BSFC improvement. Additionally, the targetintake manifold temperature and the better BSFC improvement may both beachieved in such a system. Stated another way, the target airtemperature (fresh air+EGR) at the intake manifold may now be maintainedmore accurately and consistently under all operating conditions.

FIG. 4 illustrates the modified recuperation system of FIG. 2 in moredetail. The modified recuperation system includes the boiler 220, theexpander 230, the recuperator 240, the condenser 250, the pump 270 ofFIG. 3 and additionally includes a transmission 280, an integratedstarter generator (ISG) 282, an Inverter and Control 284, aturbogenerator 286, a high temperature radiator 288, an A/C condenser290, and an accumulator 292. For some embodiments, the new heatexchanger (boiler) may replace the current air system coolers (EGR,Charge Air Cooler (CAC), and/or Inter-stage cooler (ISC)

With regard to coolants, coolants having a dry, narrow and much skewedP-h dome lead to large portion of energy contained in dry exhaust fromthe expander. This constitutes a great potential for recuperation, evenwith little superheat.

In the prior plumbing setup shown in FIG. 1, refrigerant from the pumpfirst recuperates the exhaust energy from the expander and then goes tothe boiler. The actual amount of recuperation is constrained by intakemanifold temperature, IMT, resulting in still-high-temperature exhaustenergy unused and more burden on the condenser, which limits overallBSFC improvement up to 5.5%.

In the new setup shown in FIG. 3, the refrigerant from pump goes to thelow temperature portion of boiler to ensure the IMT temperature is attarget. After heating up to a certain degree, the refrigerant isdirected to the recuperator, where a larger portion of exhaust heat canbe recuperated. For example, up to 30% of boiler total heat transfer maytake place in the low temperature portion of the boiler in the analysisbelow. Additionally, comparison of the new plumbing design (of FIG. 3)to the conventional design (of FIG. 1) shows that the new plumbingdesign results in a better cycle thermal efficiency (by approximately20%) and BSCF improvement (by approximately 1%), compared to theoriginal design at the same conditions. This is illustrated in FIGS.5-10, which illustrate the conventional system of FIG. 1 and themodified system of FIG. 3 at different operating conditions. Inparticular, in the Figures and the following description, a firstcondition, referenced as C100, describes an engine operating pointapproximating that of undergoing heavy hauling and/or acceleration.Likewise, a second operating condition, referenced as B50, describes anengine operating point approximating that of an engine cruising on ahighway

Additionally, at supercritical conditions, where the coolant'stemperature and pressure exceed a boundary point and take on propertiesbetween those of a liquid and a gas, additional changes occur. Morespecifically, supercritical conditions provide higher expansion ratio,and as anticipated, cycle efficiency is improved, but at much moremoderate margin. The selection of maximum system pressure also requiresevaluation of system weight.

FIG. 5 illustrates the previous recuperator configuration 500 operatingat C100. FIG. 5 also shows the intake air and EGR 510, boiler 520,expander 530, recuperator 540, condenser 550, and pump 560. As shown inFIG. 5, the power recovered from the expander is 21.75 kW. Additionally,the ηthermal (thermal efficiency) is 9.85%, the Pinch is 10.0 C, and theBSFC increase is 5.26%.

FIG. 6 illustrates the new recuperator configuration 600 operating atC100. FIG. 6 also shows the intake air and EGR 610, boiler 620, expander630, recuperator 640, condenser 650, and pump 660. However, as shown inFIG. 6, the power recovered from the expander is now 27.36 kW—up from21.75 kW in FIG. 5—an increase of more than 6 kW. Additionally, theηthermal is 12.39%, the Pinch is 10.5 C, and the BSFC increase is 6.53%.

FIG. 7 illustrates the new recuperator configuration 700 operating atC100 and also at supercritical. FIG. 7 also shows the intake air and EGR710, boiler 720, expander 730, recuperator 740, condenser 750, and pump760. However, as shown in FIG. 7, the power recovered from the expanderis now 28.8 kW—up from 21.75 kW in FIG. 5—an increase of more than 7 kW.Additionally, the ηthermal is 12.72%, the Pinch is 10.6 C, and the BSFCincrease is 6.69%.

FIG. 8 illustrates the prior recuperator configuration 800 operating atB50. FIG. 8 also shows the intake air and EGR 810, boiler 820, expander830, recuperator 840, condenser 850, and pump 860. As shown in FIG. 8,the power recovered from the expander is 10.84 kW. Additionally, theηthermal is 9.79%, the Pinch is 10.0 C, and the BSFC increase is 5.46%.

FIG. 9 illustrates the new recuperator configuration 900 operating atB50. FIG. 9 also shows the intake air and EGR 910, boiler 920, expander930, recuperator 940, condenser 950, and pump 960. However, as shown inFIG. 9, the power recovered from the expander is now 12.88 kW—up from10.84 kW in FIG. 8—an increase of more than 2 kW. Additionally, theηthermal is 11.66%, the Pinch is 10.5 C, and the BSFC increase is 6.44%.

FIG. 10 illustrates the new recuperator configuration 1000 operating atB50 and also at supercritical. FIG. 10 also shows the intake air and EGR1010, boiler 1020, expander 1030, recuperator 1040, condenser 1050, andpump 1060. However, as shown in FIG. 10, the power recovered from theexpander is now 14.2 kW—up from 10.84 kW in FIG. 8—an increase of about3.5 kW. Additionally, the ηthermal is 12.49%, the Pinch is 10.6 C, andthe BSFC increase is 6.87%.

1. A recuperation system including: a boiler, wherein air and exhaustgas recirculation pass through the boiler and are cooled by thermaltransfer with a coolant; an expander receiving coolant from the boiler;a recuperator receiving coolant from the expander; a condenser receivingcoolant from the recuperator; a pump pumping coolant from the condenserto a low temperature portion of the boiler; and a valve, wherein thevalve allows coolant to pass directly from the boiler to therecuperator.
 2. The system of claim 1 wherein the valve is a three-wayvalve.
 3. The system of claim 1 further including a temperature sensordetecting the temperature at the intake manifold.
 4. The system of claim3 further including a valve control controlling the valve.
 5. The systemof claim 4 wherein the valve control receives an indication of thetemperature at the intake manifold from the temperature sensor.
 6. Thesystem of claim 5 wherein the valve control adjusts the position of thevalve in response to the temperature at the intake manifold.
 7. Arecuperation method including: cooling air and exhaust gas recirculationpassing through a boiler by thermal transfer with a coolant; receivingthe coolant from the boiler at an expander; receiving the coolant fromthe expander at a recuperator; receiving the coolant from therecuperator at a condenser; pumping coolant from the condenser to a lowtemperature portion of the boiler; and actuating a valve to allowcoolant to pass directly from the boiler to the recuperator.
 8. Themethod of claim 7 wherein the valve is a three-way valve.
 9. The methodof claim 7 further including detecting the temperature at the intakemanifold using a temperature sensor.
 10. The method of claim 9 furtherincluding controlling the valve using a valve control.
 11. The method ofclaim 10 wherein the valve control receives an indication of thetemperature at the intake manifold from the temperature sensor.
 12. Themethod of claim 11 wherein the valve control adjusts the position of thevalve in response to the temperature at the intake manifold.